I know very little about the preferred way to handle trailer intermodal, other than glancing observation. This thread reminded me of the FedEx facility in Troutdale, OR. FedEx ships some of their trailers by rail, but they or the railroads seem to have no interest in loading them at the Troutdale location. Note the weed covered siding running parallel and north of the Swift and NV Transport trailer yards. This siding used to cross NW Sundial Rd and run cheek by jowl past where the FedEx ground facility is now located. The tracks were removed east of NW Sundial Rd in 2009 when construction was started on the FedEx facility.
The railroads must prefer that shippers bring their trailers to a huge centralized location for loading no matter how large the business. However I understand why the railroads would find this the ideal.
Here is a satellite view of the FedEx facility.